EFFECT OF EXTRUSION PARAMETERS ON MELT FLOW AND MECHANICAL PROPERTIES OF HIGH DENSITY POLYETHYLENE

摘要

The ability to express melt flow and mechanical properties of polymers in terms of extrusion pressure and temperature serves both the fabrication procedures and the product design. A specially designed and constructed capillary plastometer has been used to investigate melt flow characteristics, namely: shear stress, shear rate, viscosity, polymer density after extrusion, and swelling, and mechanical properties manifested as plastic flow stress. Tests were carried out on high density polyethylene (HDPE) under pressures up to 4.8 MPa and temperature range from 180°C to 280°C. Results on HDPE showed that as the extrusion temperature and/or pressure are increased, the shear stress, shear rate and swelling ratio increase whereas the viscosity decreases. The density decreases as the temperature increases and/or the die length decreases. Meanwhile, at a given temperature and die length, the flow and plastic flow stress increase with increase in pressure. At a given pressure and die length the flow increases with temperature but the plastic flow stress decreases.